1. Field of the invention
The present invention generally relates to a method for producing a film-type transmission line and a method for connecting the line, and more particularly to a reduction of impedance irregularity at a junction of a transmission line.
2. Description of the Related Art
FIG. 1 shows a conventional constitution of a junction between a film substrate and a high-dielectric substrate in a high-frequency circuit of such a radar system. Prior art generally attempts to perform ribbon bonding using a gold ribbon. A film substrate 101 and a substrate of high permittivity 102 (e.g. ceramic) are constituted of transmission line patterns 103 and 104 respectively. The film substrate 101 is placed over the substrate of high permittivity 102 and a gold ribbon 105 lying astride both of the substrates is crimped through thermocompression bonding.
A method of connection of this type is shown in Japanese Patent Laid-Open Publication No. Hei 7- 170115. In FIG. 1 of the patent document, the antenna pattern 11(A) on a film substrate 11 is connected to a circuit pattern 14 through a gold ribbon 17.
The connection through a ribbon in the prior art has disadvantages that a characteristic-impedance irregularity occurs at each junction, reflection of a signal is relatively high, and transmission loss is significant. In addition, the film substrate 101 and the substrate of high permittivity 102 are required to overlap one another as shown in FIG. 1, which causes a disadvantage of developing an impedance irregularity on an overlapped area.
Turning the film substrate 101 upside down allows patterns of both of the substrates to be connected by positioning them opposite to each other, in a face connection. As a result of this, the impedance irregularity may be reduced. However it is required to perform a bonding process through the medium of the film substrate 101 or the substrate of high permittivity 102 so that a disadvantage of lowered connecting force arises.